Broadcast switching system



P. B. MURPHY BROADCAST SWITCHING SYSTEM Jan. 6, 1942.

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BROADCAST SWITCHING SYSTEM Filed Aug. 23, 1940 l2 Sheets-Sheet 1l /NVE/v R R B. MURPH Y ATTORNEY Jan. 6, 1942. P. B MURPHY 2,269,034 l BROADCAST swlTcHING SYSTEM Filed ug. 23, 1940 12 Sheets-Sheet l2 /N/E/V Tok R MURPHY A T TORNEY Patented Jan. 6, 1942 BaoADcAsT swITCHI-NG SYSTEM Paul B. Murphy, South lNyack, N. Y., assignor Ato Bell Telephone Laboratories, Incorporated,

New York, N. Y., a corporation of'New York Application August 23, 1940, .serial No. 353,851 7 claims. lgol. 17oi) This .invention relates to program broadcasting systems and more particularly to arrangements for switching transmission lines lover which 'programs are transmitted. ,-It -is well known that a. great many 'of ythe popular programs, simultaneously broadcast by radio :stations throughout the country, originate ina single studio or at some other pick-up point, which pick-'up point is connected to the transmitters `of the various stations broadcasting the program by means of a group of interconnected wire lines. Such a group of interconnected lines, and :the transmitters which they supply, 'is referred to asa network.

There are a number of such networks known,

for example, the Red Network, the Blue Network,

tributed to another network of stations which may require three other outgoing lines from New York. The above-mentioned prog-ram vnetworks require `that the four lines rst mentioned be connected together at some centralpoint in New York, for example, in the terminal room of a telephone central office, and to the output of a voice amplifier and a iifth line, over which the programis'incoming shall be connected to the input of the same amplifier. Similar connections must also be made to a second amplier so `that the three lines comprising lthe 4second network are connected to its ,output and a line supplying the program is connected to the input.A

At the conclusion of .the foregoing programs .it may be desired Ito rearrange the above lines and add 'another line, which .at present is .connected to a third vnetwork in order t0 :establish two dil-y ferent network combinations, lone of which shall include three of the :first four lines and one of the other three lines andthe other .network shall include :the remaining line -of `the -rst 4group of four, ithe other two of :the second group and the additional fline. Since time is essential :both from the :standpoint .of continuity or broadcast and gram, the above `switching voperations must be made :as nearly instantaneous as possible.

Further it maybe desired to :establish additional networks, 4each` of which vrequires a plurality of lines, some or all of which may, or. may

` not, be `connected to other networks at the time.

f manually effected through the medium of jacks and plug-ended cords .and later by manually operated keys as disclosed and claimed in U. S. Patent 1,871,310 to A. E. Bachelet et al., issued August 9, 1932 which patented arrangement greatlyimproved and shortened the time of making the switching'transfers, yet as the volume of broadcasting has increased, andthe number of lines required to transmit the programs has increased :in proportion, it has been necessary to further improve such facilities whereby `still greater speed .and flexibility is attained.

VAn object Aof the invention .as before indicated is to provide improved means ior quickly and accurately rearranging the yirdierconnection of program lines. f f

A feature of the invention resides in means for preselecting any one or more lines .of ay group for Afuture transfer from networks to which they may be connected to other networks, a master switch corresponding to each network for. initiating said .transfers and further preselecting means for rendering said master switches Aeiiective to control said transfers either singly or jointly.

Another :feature resides in means for .preselecting any Vone or .more lines for future disconnection rom networks to which they may be connected, withoutk transfer to .another network,

under control of the master keys aforesaid.

vAnother feature fof the invention resides in means for erasing `the'preselection of a line responsive to a subsequent preselection of the ysame line 'for connection to another network.

A lfurther feature resides Yin means for simultaneously disconnecting all lines .that may be connected to a particular network.

Another feature resides in means for .preselecting ia delay, to be later introduced, between from vthe standpoint of the sponsor of the proab;

the disconnection of a line from ay connected network -and vits connection -to anothernetwork.

An understanding 4of the invention will be had ment, `embodying the `foregoing features, when read in connection with the accompanying ,drawings the `figures of which, when ,arranged in accordancefwith Fig. l13, illustrate the arrangement and circuits of switching panels `for controlling the establishment of two program networks from a total of four lines, it being understood that in practice a greater number of lines are usually involved and also facilities may, and generally will, be provided for establishing a greater number of networks, a typical installation comprising about fifteen lines and facilities for establishing about ve networks.

Referring to the drawings:

Fig. 1 shows two amplifiers, one of which is shown in detail and the other, which is a duplicate of the iirst, being merely indicated by a broken line rectangle. Each of these amplifier arrangements, which are shown and described in United States Patent 2,198,326 to A. E. Bachelet, are arranged, as described in the patent, to receive a program over one line connected to the input of the amplifier and to transmit the program properly amplified to a plurality of other lines connected to the output, the determination of which line shall be connected to the input and which lines to the output being controlled over the connected lines in the manner described in the patent. This method of control, however, forms no part of the presentinvention, it being suiicient to state that each amplifier shown forms a link for interconnecting a plurality of lines into a so-called network.

Figs. 2 and 3 show the switching relays for connecting the four lines L1, L2, L3 and L4, shown at the top of Fig. 2, to either of the network ampliers shown in Fig. 1. The small broken line rectangles, interposed between the various lines and their respective relays, shown at the top of Fig. 2, represent the necessary equipment for each line as shown for example in Figs. 4., 6, 7, 8, 11 and 13, of the beforementioned Bachelet Patent 2,198,326. Figs. 2 and 3 therefore will be understood to show the switching means whereby the lines are grouped into desired networks.

Figs. 4 to 9, inclusive, show the preselecting and switching control circuits whereby the switching relays, shown in Figs. 2 and 3, are preselected for future operation and later controlled in their operation.

Fig. 12, to the right of the vertical broken line X,.X, shows the circuits of the so-called monitors positions, one for each network, whereby control is exercised, by monitoring attendants, over the switching control circuits of Figs. 4 to 9, to effect operation of the switching relays of Figs. 2 and 3. Figs. 10 and 11 show the so-called cue preselection circuits, one for each network, whose function is to control the effective operation of the monitors circuits of Fig. 12.

Fig. 13 is a block diagram showing relative arrangement of `the other gures.

For the purpose of describing the operation of the system disclosed by the drawings, it will be assumed that switching relays 202 and 204 and 30| and 303 have been previously operated thereby connecting lines Lz and L4 to amplifier A (Fig. l) and lines L1 and L3 to amplifier B, it being understood that any group of lines connected to amplifier A will be hereinafter referred to as network A and any group connected to amplifier B as network B. Therefore, we will start our description by assuming that lines L2 and L4 are connected to network A and that lines L1 and L3 are connected to network B as indicated by lighted red lamp 501, 8 |6, 605 and 90|. Further, relays 8|'| and 902 are operated thereby opening the circuit of idle multiplepilot lamps 8|8 and 903, respectively to indicate that the respective networks are engaged.

From the drawing (Fig. 1) it will be noted that a control impulse has been received over line L4 to cause operation of relay |01 thereby connecting line L4 to the input of amplifier |00 as described in the Bachelet patent before mentioned. This, however, is unimportant, in connection with the present invention, as control of relays 20| and 202, 203, 204, 30|, 302, 303 and 304 is the only feature herein considered.

It will now be assumed that at the conclusion of the broadcast period for which the present networks were established, it is desired to maintain lines L2 and L4 connected to network A, line L1 to remain connected to network B, and to add line L3 to network A by transferring it from network B. Therefore, the control attendant, at some time well in advance of the time for changing programs, will momentarily operate keys 502, and 802 thereby operating relays 503, 803 and 804, the circuit for relay 803, for example being traced from ground, contacts of key 80|, contacts 805 of relay 803, winding of relay 803 and resistance 806 to battery. Relay 801 does not operate at this time due to the fact that ground is connected to both ends of its winding. Relay 803 in operating locks to ground at network release relay 809 in a circuit which can be traced from battery, resistance 808, winding of relay 803, contact 8|3 thereof, conductor 808, contact 205 of relay 203 and the common conductor 2|0 to ground at relay 809. Immediately following operation of keys 502, 80| and 802, these keys are released whereupon relays 503 and 804 release as their locking paths are open at contacts 20S and 201 of their respective switching relays 202 and 204, as it will be remembered that these relays are already operated thereby connecting lines L2 and L4 to network A which is the same connection desired for the next program. It is therefore immaterial whether keys 502 and 802 yare operated at all in the particular preselection which we have assumed. Due to the fact that line L1 is to be left connected to network B, itwill also be unnecessary to operate key 80|.

Returning to Fig. 8, relay 803 is now operated and locked and key 80| released. When relay 803 operated, it closed its contacts 8|0 thereby lighting the white pilot lamp 8| in series with rel-ay 8|1, as an indication that line La'has Vbeen preselected for future connection to network A. Relays 8|`| and 902 remain operated. Row pilot lamp '|02 is also lighted in parallel with lamp 8| This lamp 102 serves as a check to indicate that the particular line (L3) has been preselected in case the individual network lamps, such as 8|| should fail. When key 80| was released it removed ground from the right-hand end of the winding of relay 801, the circuit of which includes the lower back contact of this relay. Relay 801 therefore immediately operated in a circuit from battery, resistance 8|2, winding of relay 801, contacts 8| 3 of relay 803, conductor 808, fand to ground at the contact of relay 809 over contacts 205 of relay 203. Relays 803 and 801 are therefore held operated under control of release relay 889 and switching relay 203 and the white pilot lamp 8|| is lighted to indicate-that the line La has been preselected for future transfer. Should it be desired to wipe out the foregoing preselection on network A, itis only necessary to reoperate key 80| thereby short-circuiting relays 803 which releases. When key 80| is released relay 801 releases. Further, in case a preselection of a line for a particular network has been errone-'V ously made `it can .be r-.correctedby'-merely .operating the' .fpre'selection key .corresponding to the proper network.

For example, if a preselection fof Aline le for network A was l:erroneously :made and the :presee lection of 'this fline for network B was intended, the operation :of key 90.6 will .connectl :ground over contacts 901 S.of .relay 9-08,-conductor 909 and contacts -825 of relay 8-03 to short-circuit relay 003 which :therefore releases `and cin turn :releases relay' 801. When key 9.06 is released .relay f9-|0 will 'operate in the manner previously described thereby establishing the desired vproper preselection. This yarrangement prevents the preselection -of one linev to more tiranone network at the same time.

Assuming, however, that the foregoing preselection is to remain and that the transfer of line La from 'network B to network vA isnot to .be effected until the current programs on vboth networks are nished, .the 'attendant will then .make what is known las the cue ,preselection i. e., he

will momentarily operate the cue keys both network multiples corresponding to Aline Le, i. e., keys V||0| and III-02', lthereby operating the .respecti-ve relays |103 and |04. Upon ythe release of keys |.|.0| and H02, relays H05 and -|.|0.6 .respectively `will operate in the same manner .as .described for relay 801 except that Ythe holding grounds for relays H03 and H05 exist at lthe back Contact of relay l|2|8 and for relays H04 and H06 at back contacts of relay |2|9 instead of at the contacts of the preselection release relay .809. Relay H03 in operating .lights the cue preselection pilot lamp |08 zand-.relay vH04 lights the corresponding :pilot lamp and when relays |l and H06 operate, they -close a `multi-ple circuit -to light the row `pilot lamp I.

Shortly before the end of lthe present :program period the master cue control key |220 is 4operated, thereby operating relay |22| which iig-hts master Ac ue pilot lamp |222 and connects battery .to 4conductor |223 to `lig-ht the cue ready lamps and |202 at the monitors position for each network (Fig. 12) and indica-ted as monitor A :and monitor B, respectively. The circuit Yof lamp |2|l| can .be traced vfrom battery, uppermost ycontact of relay |22|, conductor |223, lamp |'2'0|, contacts of patching jack .|203 and conductors |204 and ||`|6 to ground at contact |||1 of relay |03. .The circuit .of lamp |202 .is likewise traced from battery on conductor |223, lamp |202, patching `jack |205, conductors |206 and HI8 to ground at Contact |||9 of relay H04. The lighting of lamps '|20| and |202 indicates to the monitors that the necessary cue preselect'ions have lbeen made and they may initiate the 'del sired preselected switching operations by operating the respective cue or master keys |201 and |208 when the predetermined cue is received over the loud-speakers |209 and |210, which speakers are connected to ampliers A and B over conductor pairs |2|| and |2|2, respectively.

Relay |22| locks up over its lowermost contacts to ground over release keys |224 Vand |225 in parallel, two keys :being provided in orderv to prevent accidental operation of one key from releasing the preselection circuits already established.

Operation of relay |22| also causes operation of relay 'l |20 which vcircuit can be traced from battery, contacts |226 of relay |22|, conductor |221, contact |228 of relay |2|8, conductor H24, contacts H25 of relay H03 and winding of relay of .relay |221., conductor |221., contacts .|1229 .of relay |2L|t9, fconl'luctorv f|=:|:36, :conta-cts ||31 lof relay M04, and Winding -Lof relay |f|20 -to ground. Relay |i| 20 :operating closes .a circuit to operate relay ;|\f|.:25 .which :can 4be tracedv from ground, contact '1.2.3.0.oi relay f| 22.| iront .Contact of relay |.|.20-.and .upper winding .of relay 412-25 :to battery. Relay |25 Ain :operating locks 1in .series with its lower winding .fand Fits inner lower y.contacts in a circuit trom lbattercontacts |123| of 'relay |22|, lower winding aand inner lower contact of {relay H25, conductors M28, 104 and 8|5 'to ground at the uppermost contacts .of relay 803. The operation `of :relay H 25 clos'esits .lower-most Contact thus preparing a circuit lfor .initiating operation of certain .relays .to-effect the preselectedswitoh, i. e., `to operateirelay -203 and .release relay 3103, whic-hoperation will :next be described.

When lthe program .monitors (Eig. '12),- who constantly listen `to the programs `on the networks to which tthey `are assigned by means of loud-speakers 5| 209 .and |2|0 .receive the predetermined :audible cue indicating the .close of the progran'i to which they are listening, they merely operate ya single key, key |201 in the -case of. .the monitor Aon islet/worky A .and |208 at thel monitors position l of .network .B.

Assuming Vthat lkey |201 is first operated, the cue sent .pilotlamp `|.2|.3 lights from .battery on .conductor |1223. .Operation of key |201 also extends .battery-from Aconductor |223 over contacts oipatchingjacks |.2`|4 and .conductor .|.2I5 to light .the .red ,pilot .lamp .|232 and operate `relay .I 2 |l8 in parallel. .Relay |2'|.8 locks over its contacts y|233 to ,battery .under control of relay |22 Relay 1.21.8 also opens .its inner upper contact :thereby :disconnecting xthe holding .ground from relays |y |03 and .f|.|.05 which thereupon release thereby extinguishing :lamp .fl |09. Row pilot .lamp and rrelay ||2.0,.however, vremain energized, lampr I|.||l| being .held lighted .over upper-.contacts of .relay H06 Ato battery over-lower contacts of relay H04., and .relay |20 .being .held

'over .contacts [H31 of relay H04, conductor |36,

contacts |229 of relay |2|9, conductor I|221 and contacts .|226 of relay '|22| of battery.

.It will lbe .noted at this point that .relay H20 i-s now held operated :solely .under .control of relay |.2.-|9 which is not .operated until monitor B actuates cueV key |208.

When monitor vB .receives 4the predetermined cue on .network B., .cue key |208 will fbe immediately actuated .thereby operating relay .|2|9 .in the .same manner vas previously described yfor relay '|"2.|.8, .i. e., .from .battery on yconductor |223, contact .oi key |208, patching `jack .|2|6 vand relay '|"2'.$9, `and .the vlamp |234, in parallel, to ground. Relay |`2|9 locks up .over-itslowermost contacts to .relay |22| .and .at its upper contacts releases .relays H04 and |f|0`6 and rremoves the holding batter-y .for relay 20 which now releases.

With the release of relay 'H20 the previously prepared circuit 'to effect 'the preselected switching operation is now completed which circuit l can :be traced from ground, contacts |230 olf re- H20 toi ground. A parallel operating path of v relay v| |20 is provided 'from battery, Acontacts 226 lay A|22|, lupper :back contact yof relay H20., lowermostcontact of relay H25, conductor ||34, contact "1:03 of key 104 and Winding of relay 105 tobattery Relay 105 in operating .closes its Contact 1-'06 thereby Voperating relay 101 in a circuit to ground, contacts 106 of relay 105, upper .contacts of relay 108, 4winding ofrelay101, con-y ductor 109 and contact-S1819 of relay `903 'to Lbat` tery. Relay 101 in operating closes its contacts 1|0 and 1|| thereby operating relay 1|2 over its lower winding and energizing slow relay 1|3 which starts to operate but, due to its construction delays closure of its contact for a short interval (for example three seconds) Relay 101 also opens its upper contact thereby disconnecting battery from conductors 1|6 and 904 to release relay 303 thereby disconnecting line L3 from network B. Relay 1|2 locks up over its upper winding and upper contacts to ground at the uppermost contacts of relay 803 and establishes a holding path for relay 105 from ground, lowermost contact of relay 1|2, and uppermost contact of relay 105. Relay 1|2 also connects ground at its contact 1|5 to prepare a circuit to operate relay 203 when relay 101 releases.

Following the foregoing operation which resulted in the release of relay 303, a short interval of tim-e elapses, after which relay 1|3 operates thereby closing an obvious circuit to operate relay 108 which latter relay locks up over its lower winding, lower contact and inner lower contact of relay 1|2. Relay 108 in operating opens its lowermost contacts to release relay .1!3 and opens its upper contact thereby releasing relay 101 thereby completing the previously prepared circuit to operate relay 203, the circuit of which can be traced from battery, upper contact of relay 101, conductor 82|, winding of relay 203, conductors 208 and 824, contact 822 of relay 801, conductor 823I and contact 1|5 of relay 1|2 to ground. Relay 203 in operating connects line L3 to amplier A, locks up over its contact 209 to conductor 2|0 and ground at contacts of relay 809. Relay 203 in operating also opens its contact 205 thereby opening the previously traced holding circuit for relays 803 and 801 which relays release. Further, relay 203 closes contacts 2|| and 2| 2 thereby lighting the red lamp 820, in series with relay 8|1, and operating relay 1|4 in the cut multiple selecting circuit to be referred to later. Relay 8|1 is therefore maintained operated and green pilot lamp 8|8 extinguished thereby indicating that the network A is not idle.

Release of relay 803 extinguishes lamp 8|| and 102, releases relay 1|2, and also releases relay ||25 in the cue preselection circuit. Relay 1| 2 in releasing opens the circuit of relays 108 and 105.

As soon as the switching attendant notes that all white lamps in the cue preselection panel are extinguished, i. e., H09, and he will simultaneously operate keys |224 and |225 thereby releasing relay 22| which in turn releases relays |2|8 and |2|9 and extinguishes the master cue lamp |222 thereby restoring the cue preselection circuit to normal.

The transfer of line L3 from network B to network A has now been completed and red pilot lamps 501, 820 and 8|6 are lighted under control of their respective switching relays 202, 203 and 204 and lamp 605 is lighted under control of relay 30|.

The foregoing description is based on the assumption that it was desired that a short delay be introduced between the time line Le is disconnected from network B and reconnected t0 network A, whichdelay is controlled by the twoposition key 104 which, in the position shown on the drawing, causes such a delay to be introduced. In case, however, it is desired that a substantially instantaneous transfer be effected the attendant will actuate relay 104 to its other position, prior to the time of transfer, whereby the following operations take place which differ slightly from those previously described.

When the monitors have operated keys |201 and |208 relay |20 releases as before and ground is connected to conductor H34 which immediately causes the operation of relay 101, the circuit for 101 extending from ground on conductor H34, contacts 122 of key 104, upper contacts of relay 108, winding of relay 101, conductor 109 and contacts 8|9 of relay 803 to battery. Relay 101 opens its upper contact thereby disconnecting battery from relay 303 which immediately releases to disconnect line L3 from network B. Relay 101 also closes its contact 1|| thereby operating relay 1|2 which in closing its contact 1|1 extends ground, on conductor H34, over contact 12| of key 104, to relay 108 which operates to open its upper contacts thereby releasing relay 101 which recloses its upper contact to reconnect battery to conductors 1|6 and 82|. Due to the fact that relay 1|2 is now operated, a circuit is completed to operate relay 203 in a circuit as previously described which relay in operating connects line L3 to network A and releases relays 803 and 801. The switching preselection and cue preselection circuits are restored to normal as before described. leaving only red pilot lamps 501, 820, 8|6 and 605 lighted.

Cut multiple We will next assume that line L1 is to remain idle during the next broadcast, i. e., when the present program ends it is to be disconnected from network B but not connected to another network. To effect this condition line Li will be preselected in what is known as the cut multiple, the circuits of which are shown at the bottom of Figs. 4 and 7. To preselect line L1 into the cut multip-le the attendant when making the preselection for transferring line Le to network A will also operate and release the cut multiple preselection key 40| thereby operating relays 402 and 403 in the same manner as previously d'escribed for relays 803 and 801. Relays 402 and 403 lock up to ground in a circuit from ground, Contact 305 of relay 30|, conductors 306, 606 and 508, and contacts 404 of relay 402, Relay 402 in operating lights the white pilot lamp 405 and the white row pilot lamp 406. Ground on conductor 508 holds relay 401 operated thereby maintaining the red pilot lamp 408 extinguished which is lighted when the line L1 is not connected to a network. The attendant will also, when making the cue preselections, actuate and release the one preselection key |00| thereby causing relays |002 and |003 to operate and lock to ground at relay |2|9, as described in connection with relays |04 and H06.

The joint operation of relays |002 and |003 lights row pilot lamp |004 and the operation of relay |002 connects relay |005 to the normally open contacts |226 of relay |22l, over conductor |006 and the uppermost normal contact of relay |2|9. Relay |002 in operating also lights pilot lamp |008.

When the attendant operates key 220, to place the preselected switches under control of the monitors, relay |005 operates due to closure of Contact |226 of relay |22| thereby operating relay |001, which locks up to ground at contact 409 of relay 402.

When the monitor actuates key |208, relay |2|9 operates thereby releasing relay.|005 and network B. The release of relay 30| opens itsI contact 305 thereby releasing relays 402 and 403 and also relay 407 which operates when relay 30| was first operated. Relay 402 in releasing extinguishes pilot lamp 405 and the release of relay 401 lights pilot lamp 408 to indicate that line L1 is not connected to any network.

Manual transfer If desired the attendant can, subsequent to the preselection of any line for connection to any multiple, cause the transfer to be effected at once, on a fast or slow basis, by manually operating a switch key individual to the line. For example, if for any reason it is desired to cause the immediate transfer of line L3 from network B to network A before the end of the program, the attendant can operate key '|04 to condition the circuit for a fast transfer and then operate keys 'H8 and 1|9 simultaneously. The function of key H9 is to ground the common conductor |20 only during the act of effecting a manual transfer, i. e., at the time key 'H8 for example is operated, thus preventing a false transfer due to the accidental operation of one of the manual switching keys. Simultaneous operation of keys 'H8 and H9 connects ground over contacts |22 of key 104, to operate relay '|01 thereby releasing relay 303 and immediately operating relay 203 in the same manner as previously described when the transfer was effected by operation of keys |201 and |208 at the monitors position. The extinguishing of lamp 90| and the lighting of lamp 820 is an indication to the attendant that the transfer has been effected.

In case it is desired to immediately disconnect line L3 from network B without connecting it to network A the attendant before effecting the manual transfer above described will preselect line L3 into the cut multiple of that line by momentarily operating key 123.

Disconnectz'on. of a network In case it is desired, for any reason, to simultaneously disconnect all lines from a particular network to which they may be connected the attendant can operate the release key common to the particular network, i. e., key 8|4 for network A or key 005 for network B. Operation of key 8|4, for example, causes operation of relay 800 bination, means for preselecting and preparing circuit arrangements to control said switching means to rearrange the interconnection of said lines as desired, a master switch for each group for completing said prepared circuits, and other preselecting means for rendering said master switches effective, either singly or in any desired combination, to effect said rearrangement.

2. A system in accordance With claim 1 characterized by other preselecting means, individual to each line, for conditioning said circuit arrangements to disconnect the preselected line from a connected group, but prevent its recon-` nection to another group in response to operation of said master switches.

3. A system in accordance with claim 1, characterized by means responsive to a second preselection of any line for transfer prior to the completion of said transfer, to cancel the preselection previously made.

4. A system in accordance with claim l, characterized by release means common to each group for simultaneously disconnecting all lines from the respective group.

5. A system in accordance with claim 1, characterized by means individual to each line for introducing a time delay between the disconnection of the respective line from one group and its reconnection to another group.

6. In a communication system, a plurality of lines, a plurality of amplifiers, a relay individual to each amplier for each line, each relay being arranged, when operated to interconnect the respective amplifier and line, manually controlled preselecting means individual to each relay adapted, when operated, to prepare a circuit for causing the release of any operated relay associated with the respective line and the subsequent operation of the relay corresponding to the preselecting means, a master switch for each amplier, and other manually controlled preselecting means for rendering sai-d master switches efwhich disconnects ground from the common conductor 2|0 thereby releasing all switching relays (20|, 202, 203 and 204) which may be operated and locked to this conductor. rlhis operation also releases any preselection relays, such as 803 and 801, which may have been operated.

What is claimed is:

1. In a communication system, a plurality of lines, switching means for interconnecting said lines into independent groups in any desired comfective in any desired combination, subsequent to the preparation of said relay circuits, to complete said circuits. l

'7. In a communication system, a plurality of' lines, switching means for interconnecting said lines into independent groups in any desired combination, means for preselecting and preparing circuit arrangements to control said switching means to rearrange the interconnection of said lines as desired, a master switch for each group for causing the completion of said prepared circuits, other preselecting means for rendering said master switches effective, either singly or in any desired combination to effect said rearrangement, further preselecting means, individual to each line, for conditioning said circuit arrangement to disconnect the preselected line from a connected group and prevent its reconnection to another group in response to operation of said master switches, and means responsive to a second preselection of any line, prior to completion of a switching voperation to vcancel the preselection previously made.

PAUL B. MURPHY. 

